Genes, Antigens, Antibodies, and Basic Testing Flashcards
Leucocyte Poor Red Cells
Used primarily for patients with repeated febrile non hemolytic (FNH) reactions or those that are chronically transfused
Usually due to the presence of cytokines released from white cells or alloimmunization to HLA or leukocyte antigens
Differentiating A1 and A2
Based on reactivity differences with anti-A1, lectin from Dolichos biflorus, which agglutinates A1 but NOT A2 cells
Anti-H Differentiation
Lectin from Ulex europaeus, which will agglutinate O cells (HH or Hh), but not Bombay cells (hh)
Se gene
Two alleles, Se (secretors) and se
Allow expression of ABO and H (A, B, H, and Le^b) antigens in body fluids
Combination of H and Le genes
H and Lea will be on red cells, only Lea only in saliva
Combination of H, Se, and Le genes
H and Leb on the red blood cells, H, Leb, and Lea in small amounts in body fluids
Rh null
No D, C, E, c, or e antigens on cells, associated with hemolytic anemia as these structures are associated with RBC membrane integrity
Inheritance of 2 nonfunctional RHCE alleles with deletion of both RHD alleles
OR homozygous recessive inheritance of the regulator RHAG with normal RHCE and RHD
Deleted cells (D–)
Missing some or more of the normal Rh alleles
Doesn’t react with anti-E, anti-e, anti-C, or anti-c
Rh antibodies
Typically RBC stimulated
Pregnancy (cause hemolytic disease of the newborn as they cross the placenta)
Transfusions (will cause transfusion reactions)
IgG, do not activate complement, will not agglutinate saline suspended RBCs unless IAT is used
C/e and E/c are usually together
Lewis Antigen Creation
Includes plasma antigens that absorb onto RBCs
Lewis antibodies
IgM, usually only in Le(a-b-) patients, can be temporarily seen during pregnancy
Landsteiner’s Rule
If an individual has the antigen, they will not have the antibody
ABO Expression/makeup
Can be secreted if the proper genes are present, glycolipids or glycoproteins, develop into full expression between 2-4 years of age
H antigen
H gene contains the alleles H and h, it is the building block for A and B antigens
Antigen is a sugar acceptor, with A and B accepting different sugars and O accepting none
Anti-A and anti-B
IgM and therefore able to activate complement, causing agglutination
Problems with Forward Typing
(Extra antigen, weak antigens)
- ABO subgroups
- Acquired B phenotype
- Bone marrow/stem cell transplants
- Polyagglutination
- Rouleaux
- Transfusion of non-specific blood
Problems with Reverse Typing
(unexpected antibodies or weak/missing antibodies)
- A subgroups with Anti-A1
- Cold alloantibodies
- Elderly
- Newborns
- Rouleaux
Bombay Phenotype
Types as an O, with alloanti-H that can activate complement and cause hemolysis
Can transmit functional A and B genes to their children, even though they can’t produce them themselves
Rh Genes
Controlled by RHD (D expression) and RHCE (C, c, E, e)
Fisher-Race Terminology
Rh antigens, D, C, c, E, e, Cw, G,…
Wiener Terminology
Rh haplotype terminology, R1, R2 for CDe/CDe
Weak D
Weak D testing is carried out on any cell that previously gave a negative reaction with anti-D and Rh control
Caused by weaker expression of the cDe haplotype, from the C antigen is inherited trans to the D antigen
Can be transfused with D-Neg blood
Partial D
Lacking 1 or more epitopes of D antigen, and makes antibody for missing parts
Type as D Pos, create Ab after transfusion or pregnancy
F/ce antigen
Expressed when c and e are on the same haplotype
Ce/rhi antigen
Expressed when C and e are on the same haplotype, D-Pos patients who make anti-C
Cw antigen
Low frequency antigen
V/ces antigen
30% prevalence in African Americans
G antigen
Appears anti-D and anti-C
DAT
Use AHG (antihuman globulin) to detect IgG and complement, which indicates the possibility of immune mediated hemolysis in the patient, done for:
- autoimmune hemolytic anemia
- HDN (hemolytic disease of newborn)
- Drug-related mechanism
- Transfusion reaction
Antibody Screen
For patients needing transfusions, pregnancies, donors and those having transfusion reactions; uses O donor cells with known antigens
Hemolytic Disease of the Newborn
D- mothers makes antibodies to D+ baby in first pregnancy, newborns show positive DAT, increased serum bilirubin
2 - 5% Washed Red Cell Suspension
Visibility of antigen and antibody complexes is dependent on the number of antigen sites available
Grading Reactions with Anti-A and Anti-B
Anti-A and anti-B are saline- reactive antibodies, saline reactive antibodies are most often of the IgM class and react strongly at room temperature, and strongest at 40 C.
Antiglobulin Test
DAT
- Detects in-vivo sensitization of IgG alloantibodies
- IgG autoantibodies
- Complement components
(IAT is in-vitro)
For antiglobulin tests, why do you Incubate RBCs with antisera?
Allows time for antibody molecule attachment to RBC antigen
For antiglobulin tests, why do you Centrifuge?
Accelerates agglutination by bringing cells closer together
Albumin Reaction Media
Allows sensitized cells to come close together to form agglutination lattices
PeG Reaction Media
Concentrates Ab and creates a low-ionic sln that allows greater Ab uptake
ABO gene locus
C’some 9
Antigen Development
A and B develop 5th week fetal life, but increase slowly, formed from complex interaction of H/h and ABO genes
Type 1 Precursor Chain
Glycoprotein precursor of ABH Ag
Type 2 Precursor Chain
Glycolipid precursor of ABH Ag on RBC surface
ABO Ab
- Usually IgM, can be IgG/IgA in small quantities
- React best at RT
- Activate complement (including the IgG at RT)
- Saline agglutinins
Anti-A,B
IgG form is found in serum from sensitized O Pts (i.e. O mothers carrying A or B fetuses), which can cause HDFN
Anti-H
A weak, cold reacting Ab in A1, A1B people
Anti-A1
Non-recative a Body Temp so Clinically Insignificant, if it is reactive at that temp, it can cause in vivo RBC destruction and is clinically significant
Weak/Missing Ab
Most frequent cause of ABO discrepancy
Low ABH Ab titers are found in the young, sick or debilitated and will not be picked up by routine testing, corrected by optimizing the reverse reaction conditions such as lower temp. (A/C and O cells should be controls)
Weak/Missing Ag
A/B subgroups, or weakening Ag strength in conditions like Leukemia
Acquired B Phenotype
Can be caused by intestinal obstruction, carcinoma in colon/rectum, any gastrointestinal disorder that obstructs or slows movement, allowing intestinal bacteria into bloodstream
Weak D Genetics
Caused by many different changes in the RHD gene, Types 1, 2, and 3 are 90% of the cases found in Europeans
Compound Ags
Are directed to the shared epitopes of C/c or E/e on the same protein
Immunogenicity of Rh Ag
D is most immunogenic, e is the least
Rh Testing
Use antisera that has been chemically modified with a sulflhydryl compound that weakens the disulfide bonds at the hinge region and allows the IgG to flex
